Process for the cracking treatment of hydrocarbons



A. D. SMITH Feb. 1s, 1936.

PROCESS FOR THE CRACKING TREA'IWIEHI'J1 OF' HYDROCARBONS Filed July 2, 1934 Mlm@ Patented im;y is, 193e y UNITED STATES PROCESS FOB THE CBACKING TREATMEN 0F HYDROCARBONS ammiy n. smiiii, rmi man, ni. Application Juiy z, 1934,serigi N0. 733,479

13 Claims.

l The invention relates to improvements in process and apparatus for the cracking treatment of hydrocarbons and particularly to a process for the continuous production of gasoline of superior quality from heavier petroleum hydrocarbons wherein a portion of an intermediately derived stock, so treated as to be tolerant of the cracking conditions imposed, is returned to such cracking cycle.

A process for the production of gasoline has been proposed wherein a composite stock comprising a virgin fraction, and an intermediately derived residual fraction partially clarified through sedimentation, is subjected to cyclic cracking conditions; but such process has never been extensively developed due to deposition of carbon in the cracking coil. Y

The carbon diiliculty has been partly solved by eiecting an intermediate separation of the cracking stock into distillate and residual fractions, with resubjection of the distillate fraction only to cracking conditions; but such method has fallen somewhat short of 'the desired optimum through unnecessary fuel expenditure and lower octane value of the gasoline produced than would have obtained under inclusion of a material quantity of a residual fraction in the crackingbody.

The present process retains the advantages of distillate cracking and improves the quality of the gasoline produced by segregating the products of a cracking reaction into a vaporlzed fraction and an intermediate residual fraction, followed by resubjecting to such cracking reaction the heavier portions of the vaporized fraction admixed with a material portion of the intermediate residual fraction sov treated as to be tolerant of the cracking conditions imposed.

To obtain the above objectives the cracking operation is continuously conducted in any conventional type of cracking coil releasing to a vapor separator. The cracking stream, carrying in suspension a finely divided mineral adsorbent of selective adsorptive power towards carbon I and/'or carbon forming substance, is substantially the cracklng'stream, is continuously admixed a special ilnely divided mineral adsorbent, relatively large in quantity to the amount carried by the cracking stream, and which while possessing the gsame general adsorptive characteristic of the former is of heavier specific gravity. Such special adsorbent' oiiers a fresh and highly active surface to the reacting streams as the one is reduced and the other elevated to approximately an incipient cracking temperature, thus supplementing the adsorptive effect of the more or less spent adsorbent derived from the cracking stream at the critical point of tendency towards separation oi elementary carbon. In actual practice introduction of the adsorbent carrying raw stock to the cracking stream is effected through contiguous manifold connections, which-including the indirect cooling means-are so closely pre or postjacent the cracking coil release valve, that cooling, inhibition of cracking, introduction of special adsorbent, release and discharge of the admixed adsorbent laden stream to the vapor separator are all practically concurrent and cofrrelated operations.

The cooled and released stream immediately enters the primary vapor separator which is preierably constructed in vertical, cylindrical form and provided. with a vertical baflie dividing the separator into two sections, each open` at either end for the iiow oi' vapor and liquid respectively. A suiiiciently reduced pressure is maintained within the separator to admit 'oif the separation and vaporization ofthe desired light fractions; the latter being conducted to a bubble tower of standard design. l

The special adsorbent, intimately dispersed in the vaporous mist following release of the admixed stream immediately begins to gravitate to the bottom of the separator; the descending particles forming an adsorptive and cleansing rain or nuclei for the separating globules and droplets of liquid, at the same time dragging downwith them the particles of lighter more or less spent adsorbent and associated carbonaceous impurities derived from the cracking stream.

The adsorptive action most eilicient with initial contact, is also highly effective during the descent of the adsorbent through the intermediate loam layer preceding liquid unity; the separator being maintained at such temperature within the proscribed limits of vaporization and pressure that mild polymerization continuously progresses with the concurrent adsorption of the complexes produced by the adsorbent employed, care being taken through a suitably controlled time factor to preclude any post reactions advancing to the state of free carbon formation.

The spent adsorbent with its associated impurities and a minimum amount of carrying oil is continuously withdrawn from the base of the vapor separator, the supernatant layer of the intermediate residual fraction on the discharge side of the vertical baille obtaining as a de-polymerized or tolerant stock capable of forming a material fraction of the -stock supplied to the cracking coll. Such tolerant stock is conveniently withdrawn from the separator at selective levels precluding any substantial percentage oi' spent adsorbent being returnedl to the cracking system; the withdrawn oil being continuously conducted to the base of the bubble tower to unite with the heavier distillate fractions separated therein. The composite stock thus formed, admixed with its appropriate adsorbent, is continuously returned to the cracking cycle and the process repeated as before described.

While the raw stock may be introduced solely as a cooling oil in the manner previously described, and the tolerant stock be so reduced that a portion thereof may be diverted as specification fuel oil, I prefer to concurrently subject a portion of the raw stock, admixed with a portion of the tolerant residual fraction reduced short`of fuel specification and withdrawn from the primary vapor separator at a somewhat lower level than the fraction conducted to the bubble tower, to material preheating; employing with such admixture an adsorbent of selective associative action towards natural asphaltenes as well as pyrogenically formed complexes, thus securing progressive pre-adsorption of potential carbon forming bodies without active cracking temperatures being developed.

Under such preferred method of operation, the preheating of the admixed raw stock and tolerant fraction may be conveniently carried out in a pipe still, preferably consisting of a heating coil disposed in the same furnace as the cracking coil; the admixed stock being heated to approximately an incipient cracking temperature and released to a secondary vapor separator. The withdrawn spent adsorbent from the primary vapor separator is continuously pumped to such released stream; it being noted that substantially the entire amount of adsorbent introduced at various points of the system thus passes to the secondary vapor separator as spent material.

The temperature of the released stream, as iniluenced by the somewhat cooler stream of spent adsorbent and its carrying oil derived from the primary vapor separator, is so correlated to the reduced pressure maintained in the secondary vapor separator that the residual fraction separating therein is of commercial fuel specification after removal of. adsorbent by sedimentation; the vaporous fractions passing to the bubble towler and forming a considerable portion of the distillate complement of the composite stock returned to the cracking coil.

The gasoline fractions are recovered from the bubble tower according to standard practice and provision may also be made at this point for withdrawing other light fractions from the system not desired to be returned to the cracking coil.

The fuel oil carrying the final spent adsorbent is continuously withdrawn from the base of the secondary vapor separator under a time factor preventive of undesirable after reactions, cooled, and subjected to sedimentation in any conventional type of settler, preferably a horizontal bafa,os1,sss

fied means from which adsorbent may be intermittently, or continuously withdrawn under automatic control; the clarified fuel being conducted to storage for i'lnal settling of traces of adsorbent.

Referring to the character of the adsorbents employed it may be stated at this point that the use of a finely divided mineral adsorbent of characteristic adsorptive action towards carbon and/or carbon forming substance, while dispersed in a cracking body or cracking stream of oil, is the subject of a pending U. S. application. Serial No. 723,144, illed June 30, 1924; the present invention being an improvement over the therein described methods of employing adsorbent, in the particular choice of adsorbent for a speclflc purpose, and generally in the novel result obtained; i. e., the productionaof an intermediate residual fraction tolerant to cracking conditions commonly employed ln the art.

As a mineral adsorben g selective associative power towards carbon and/or carbon forming substance, may be mentioned lime. fullers earth, alkaline earth oxides, alumina, kaolinite, bentonite, coke, coal, inert earths, clays of various types, heavy spar, magnesite, bauxite, kieselguhr, silica-gel and the various oxides of iron, but I prefer to employ lime in the form of lime hydrate in the cracking coil, a mixture of such hydrate and fullers earth flour, with the lime predominating, during preheating; and as the special adsorbent, lime hydrate (colloidal or non-colloidal)v and/or fullers earth ilour. The selection is based partly on account of the ready accessibility and cheapness of the adsorbents recommended, but principally on account of their high adsorptive and associative power towards resinous carbon forming substance and from the fact that they may be procured in varying specific gravities and/or physical structure.

Further, lime hydrate loses approximately '15% of its water of constitution somewhat below the cracking temperatures commonly employed in the art; the theory being offered that release of such water forms ultra microscopic fissures and vpores in the lime particles highly beneficial in the treatment involved. Possibly a certain amount of absorption of still soluble petrolenes and carbenes occurs in conjunction with the preadsorption of asphaltenes or other highly complex hydrocarbon polymerides.

The employment of non-colloidal lime hydrate in a cracking cycle to achieve a ready separation of such adsorbent and its associated carbon products from a final residuum has been proposed in U. S. Patent No. 1,913,619, but where the rate of settling is below a commercial optimum, such patent mentions filtration as a method of separation. The present invention maintains a commercial optimum in the rate of settling, thus avoiding any 'necessity of filtration, through admixture of sumcient fullers earth ilour with the lime hydrate (preferably in non-colloidal form) as to insure a specitlc gravity dominating internal friction; the ratio of fullers earth being increased to the complete exclusion of the lime hydrate if the nature of the residual fraction so requires. Fullers earth can be moreover readily obtained in varying densities and degrees of ilneness, thus enabling agrade to be selected best suited for the particular conditions involved.

The quantity of adsorbent employed will depend on its chemical composition, degree of fineness, density and physical structure, the extent of cracking, preheating and post-polymerization 1 practiced, as well as the nature of the raw stock. In general from one-quarter to one pound of adsorbent per barrel of oil treated will be ample for the oil'charged to the Acracking coil, approximately the same quantity during preheating, and from one-half to two pounds for the special adsorbent; a total of two and one-half pounds for the three concurrent operations being usually suicient in comercial practice. In each instance the adsorbents are preferablyjnitially incorporated in separate mixing tanks with relatively small quantities of the respective oils undergoing treatment; the slurries thus produced being continuously fed Ain predetermined amountsl to the respective means involved by methods well known in the arts.

Apart from 'the hypotheses advanced, explanations given and quantities of adsorbent mentioned, the significant fact remains that where there concurrentlyexists adsorption of carbon and/ or carbon forming substance in the cracking coil, pre-adsorption of potential carbon forming substance during pre-heating and post-adsorption of carbonaceous products formed under incipient cracking conditions, a more than merely additive result is obtained as evidenced by the improvement in the `quality of gasoline produced,

the relatively small total quantity of adsorbent required, and the highly important production of an intermediate residual fraction which, when freed from spent adsorbent and its associated impurities, may be continuously returned in a material quantity to the cracking cycle. The importance of being able to resubject to such cycle a product having a preponderance of double bond hydrocarbon compounds, such as usually obtains in the tolerant residual fraction, cannot be over estimated in the production of gasoline of high anti-knock value. f

Further while the degree of tolerancy of the clarified residual fraction to cracking conditions is obviously limited by the extent of the cracking obtained per pass, the temperature and pressure carried in the cracking coil, as Well as by the nature of the raw stock itself, the improvements in process herein described admit of introduction to the cracking coil of a composite stock containing from 10% by volume of clared residual stock under severe liquid vapor phase cracking treatment up to 45% and over under favorable conditions; 30% being a fair average and the minimum 10% a decidedly material quantity. Further the saving in heat due to minimizing the thermal units absorbed in unnecessary vaporization incident to maximum distillate separation is considerable. Other advantages will occur to one skilled` in the art.

In order that the invention may be better understood, reference is made to the attached drawing where Fig. l represents in diagrammatic form an apparatus suitable for carrying out the process; and wherein a high pressure charging pump I, supplied through the line 2 with composite stock from the bubble tower '3, delivers such charging stock via lines 4 and 5 through the preferably parallel flow type of heat exchanger 6 to the cracking coil 1 disposed in the furnace 8. The pump 9, supplied with adsorbent (lime) slurry from the mixing tank IIl, delivers such slurry at a predetermined rate through an extension of the line 4, as controlled by valive II, to adm ix with the charging stock as it enters the line 5;

ing carried in phase.

The converted stock from the cracking coil I is released via the transfer line I2, through the heat exchanger 6 and lines I3 and I4 as controlled by the cracking coil release valve I5, to the primary vapor-separator I6. The pump I1, supplied through the line I8 with the cool raw stock to be converted from the tank I9, as controlled by valve 2U, delivers such stock via'lines 2|, 22 and I3', as controlled by valve 23, to admix with the cracking stock and effect a reduction in temperature thereof inhibtive of further carbon formation substantially at the point where the latter is released from the heat exchanger and thepressure of the cracking coil. The pump 24, supplied with adsorbent (lime and fullers earth, or fullers earth) slurry from the mixing tank 25, (fed with oil from the tank I9, as control-led by valve 26) delivers such slurry at a predetermined rate through the line 22 as controlled by valve 21, to enter the line I3; thus insuring a proper amount of adsorbent being carried in suspension by the cooling oil as it contacts the cracking stream, and a sufficient excess to act as a. depolymerizer in the vapor separator. If desired a portion of the raw stock employed as a cooling oil may be moderately preheated by diverting a part of the flow of line ZI to line 28, as controlled by valve 29, through the heat exchanger 30, and thence by line 3I to the line I3.

The primary vapor separator I6, into which the cooled and adsorbent laden stream from the cracking coil is released, is provided with a median, vertical baiile 32, dividing a substantial portion of such separator into two open end sections 33 and 3,3' respectively. The vapor line 34 conducts the separated vaporous fractions to the bubble tower 3 while the Withdrawal line 35, as controlled by valve 36 (preferably of automatically operatedtype) provides for the removal of the spent` adsorbent and itsassociated impurities asl it subsides to the bottom of the separator. Disposed on the vertical shell of the section 33' at suitable levels insuring adequate settlement, are the selective Withdrawal lines 31, 38 and 33 as controlled by their respective valves 3l', 38' and 39' for release of the supernatant, tolerant residual stock; such lines connecting to the flow line 40 which conducts the de-polymerized or tolerant stock through the down-comer 3' to the base of the bubble tower 3, from whence, admixed with the heavier distillate fractions condensed therein, composite charging stock is returned to the system as previously described.

In the preferred method of operation a portion of the raw stock delivered by the pump Il and moderately preheated in its passage through the heat exchanger 30, is fed through the line 4I to the discharge side of the .pump 42; the valve nest43 and 44 affording control of the fractions delivered to lines I3 and 4I respectively. Adsorbent slurry is supplied to the fraction of the raw stock fed through line 4I by pump 24 via lines 22 and 45, as controlled b-y valve 45'; the valve nest 21 and 45' admitting of selective quantities of adsorbent (lime and fullers earth, or fullers earth) being supplied to the respective raw suspension during the cracking stock fractions, as will be apparent to one skilled ant stocks as delivered through line 41 may ref ceive a further increment of adsorbent (lime) supplied by pump .I through lines I and Il, as controlled by valve 49. 'I'he final admixed stream then passes to the preheating coil 80 disposed in the cooler portion of the furnace 8. from which coil the admixed stock, raised to an incipient cracking temperature, is discharged through the line 5l, as controlled by the pressure release valve B2, to enter the secondary vapor separator 53; the discharged oil receiving in its passage to such separator the spent adsorbent withdrawn from the base of the primary separator through the line 35 with introduction thereof to the line 5| being effected by pump 5l and line 54'.

Specification fuel oil and spent adsorbent. is continuously withdrawn from the settling well 53' of the secondary vapor separator 53, through line 55 as controlled by valve I5' (preferably of automatic type), and thence through cooler il and line 58 to enter the horizontal settler 51. From the latter, spent adsorbent is withdrawn by lines 5B and 58', as controlled by valves 59, 60 and 6|, through cooler 62 to be discharged from the system as a waste product. 'I'he supernatant, clarified, specification fuel flowing over baille 51' is continuously withdrawn from the system through line 83,'as controlled by valve 6l, and pumped by pump il through cooler 80 to storage.

Vapors generated in the settler 51 escape through the line l1 to the bubble tower l. The vapor line 68 conducts vaporous fractions released in the secondary vapor separator I3 through the outer Jacket of the exchanger 30 to enter the line Il, and thus pass to the bubble tower 3 along with vaporous fractions from the primary vapor separator Ii.

The bubble tower 3 which is of standard construction may be provided with an intermediate stripping device (not shown) for removal of relatively heavy light fractions, such as for instance kerosene distillate; the light gasoline fractions -escaping through vapor line 5l to be condensed by condenser 10. The liquefied gasoline ilows through line 1I to receiving drum 12,v from whence a fraction of the condensate may be returned through line 13, pump 1I and line 15 terminating in the perforated coil 18 to serve as trim stock. Uncondensed gas escapes through line 11, as controlled byA valve 1l, (preferably of automatic relief` type) while the preferred gasoline is withdrawn from the system by line 19 as controlled by valve Il.

As an example of operative temperatures and pressures, the convertedstock leaving the cracking coil may obtain at 900 F. under 500 lbs. pressure, and the tolerant residual stock may be withdrawn from the primary vapor separator at 675 F. under '75 lbs. pressure, while the secondary vapor separator is .maintained at approxi- 'mately '780 F.; but it is to be clearly understood that such values are to be considered illustrative only of conditions that may prevail; the process generally admitting of the widest divergent temperatures and pressures commonly practiced under liquid-vapor phase cracking. The process is moreover not limited to the particular type or relative size of the apparatus herein shown, nor to the exact quantities of adsorbent mentioned, which are given for purposes of example only. It is to be further understood that the apparatus is equipped with the usual safety valves, indicating and recording pressure and temperature gauges, liquid level controls, etc., commonly eml ployed in the arts.

What I claim is new and desire to protect by Letters Patent is:

1. A procesrfor converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting said oil commingled with finely divided s mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said oil simultaneously with reduction in temperature thereof to anvincipient cracking stage finely divided mineral adsorbent of the same general characteristics but heavier than said lnrst mentioned adsorbent, substantially concurrently with such reduction in temperature releasing the so treated oil to a zone of reduced pressure. and separating therein respectively as vapor and liquid under accelerated sedimentation by .such heavier adsorbent said lighter hydrocarbon and a clarified residual fraction employable as fuel oil without further treatment.

2. A process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting said oil commingled with finely divided mineral adsorbent towards carbon forming substance, such as lime, to a cracking temperature under superatmospheric pressure, admixing with said oil simultaneously with reduction in temperature thereof to an incipient cracking stage additional ilnely divided mineral adsorbent of the same general adsorptive characteristics but heavier than said first mentioned adsorbent, such as fullers earth, substantially concurrently with such reduction in temperature releasing the so treated oil to a zone of reduced pressure, and separating therein respectively as vapor and liquid under accelerated sedimentation by such heavier adsorbent said lighter hydrocarbon and a lclarified residual fraction employable as fuel oil without further treatment.

3. A process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting said oil commingled with finely divided lime to a cracking temperature under superatmospheric pressure, admixing with said oil simultaneously with reduction in temperature thereof to `an incipient cracking stage finely divided fullers earth in quantity relatively large to said lime, substantially concurrently with such ad- -mixture releasing the so treated oil to a zone of reduced pressure and separating therein respectively as vapor and liquid under accelerated sedimentation by said fullers earth said lighter ,hydrocarbon and a claried residual fraction employable as fuel oil without further treatment.

4. A process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting said oil commingled with finely divided lime to a cracking temperature under superatmospheric pressure, admixing with said oil simultaneously with reduction in temperature thereof to an incipient cracking stage finely divided heavy spar in quantity relatively large to said lime, substantially concurrently with such admixture releasing the so treated oil to a zone of reduced pressure and separating therein respectively as vapor and llquidunder accelerated sedimentation by said heavy spar said lighter hydrocarbon and a clarified residual fraction employable as fuel oil without further treatment.

5. A process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting said oil commingled with nely divided lime to .a cracking temperature under superstmospheric pressure, admixing with said oil simultaneously with reduction in temperature thereof to an incipient cracking stage finely divided lime with a dominant quantity of heavier adsorbent substantially concurrently with such admixture releasing the so treated oil to a zone of reduced pressure and separating therein respectively as heavier than said rst mentioned adsorbent, subfrom saidoil and commingled with nely divided mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said composite stock such volume of cooler said heavier hydrocarbon oil commingled with finely divided mineral adsorbent of the same general adsorptive characteristics but heavier than said first mentioned adsorbent as to reduce the temperature of said stock to an incipient cracking stage, substantially concurrently with such reduction in temperature releasing the admixed stream to a zone of reduced pressure, separating therein respectively as vapor and liquid under accelerated sedimentation by said heavier adsorbent said. lighter hydrocarbon and a claried residual fraction, and returning said claried residual fraction as a portion of said composite stock to cracking conditions as aforesaid. Y

8. A cyclic process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting a composite stock derived from said oil and 'commingled with finely divided mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said composite stock such volume of cooler said heavier hydrocarbon oil commingled with finely divided mineral adsorbent of the same general adsorptive characteristics but heavier than said rst mentioned adsorbent as to reduce the temperature of said stock to an incipient cracking stage, substantially concurrently with such reduction in temperature releasing the admixed stream to a zone of reduced pressure, separating therein respectively as vapor and liquid under accelerated sedimentation by said heavier adsorbent said lighter hydrocarbon and a clarified residual fraction, dephlegmating said vapor into gasoline and distillate, admixing with said distillate said clariiied residual fraction and returning such admixture as said composite stockrto cracking conditions as aforesaid.

9. A cyclic process for converting heavier hydrocarbon oilinto lighter hydrocarbon which comprises subjecting a composite stock derivedy from said oil and commingled with nely divided lime to acracking temperature underV superatmospheric pressure, admixing with said composite stock such volumeof cooler said heavier vhydro-k carbon oil commingled with finely divided fullers earth in a relatively large quantity to said lime as to reduce the temperature of said stock to an incipient cracking stage, substantially concurrently with such reduction in temperature releasing the admixed stream to a zone of reduced pressure, separating therein respectively as vapor and liquid under acceleratedV sedimentation, by

said heavier adsorbent said lighter hydrocarbon and a clarified residual fraction, dephlegmating mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said composite stock such volume of cooler said heavier hydrocarbon oil commingled with finely divided mineral adsorbent of the same general adsorptive characteristics but heavier than said rst mentioned adsorbent as to reduce the temperature of said stock to an incipient cracking stage, substantially concurrently. with such reduction in temperature releasing the admixed stream to a zone of reduced pressure, separating therein respectively as vapor and liquid under accelerated sedimentation by said heavier adsorbent said lighter hydrocarbon and a clarified residual fraction, subjecting a portion of said clarified residual fraction admixed with said heavier hydrocarbon 'oil commingled with said heavier adsorbent to incipient cracking conditions, releasing such admixture together with spent adsorbent discharged from said zone of reduced pressure to a zone of less pressure than preceding, separating therein respectively as vapor and liquid additional distillate and adsorbent containing residuum, subjecting said residuum to accelerated sedimentation productive of a clarified fuel oil, uniting the vapors of said additional distillate and said lighter hydrocarbon and dephlegmating therefrom gasoline and a residual distillate, admixing with said residual distillate a portion of said clarified residual fraction and returning such admixture as said composite stock to cracking conditions as aforesaid.

11. A cyclic process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting a composite stock derived from said oil and commingled with finely divided lime to a cracking temperature under superatrnospheric pressure, admixing with said composite stock such volume of cooler said heavier hydrocarbon oil commingled with finely divided fullers earth in quantity relatively large to said lime as to reduce the temperature of said stock to an incipient cracking stage, substantially concurrently With such reduction in temperature releasing the admixed stream to a zone of reduced pressure, separating therein respectively as vapor and liquid under accelerated sedimentation by said heavier adsorbent said lighter hydrocarbon and a clarined residual traction. subiecting a portion oi.' said claridad residual traction admixed with said heavier hydrocarbon oil commingled with iullers earth to incipient cracking conditions, releasing such admixture together with spent adsorbent discharged from said zone of reduced pressure to a zone of less pressure than preceding. separating therein respectively as vapor and liquid additional distillate and .adsorbent containing residuum, subjecting said residuum to accelerated sedimentation productive of a clarified i'uel oil, uniting the vapors o1 said additional distillate and said lighter hydlocarbon and dephlegmating therefrom gasoline and a 'tesidual distillate, admixing with said residual distillate a portion oi said clarined residual fraction and returning such-admixture as said composite stock to cracking conditions as aforesaid.

12. A ,process for converting heavier hydrocarbon oil into lighter hydrocarbon which will subjecting said oil commingled with finely divided mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said oil while at said cracking temperature finely divided mineral adsorbent of the same general adsorptive characteristics but heavier than said l'st mentioned adsorbent. substantially concurrently with such admixture reducing the temperature oi' said a,osi,ssc

oil to an incipient cracking stage and releasing to a zone o! reduced pressure, and separating therein respectively as vapor and liquid under accelerated sedimentation by such heavier adsorbent said lighter hydrocarbon and a clarified residual traction employable as fuel oil without further treatment.

i3. A cyclic process for converting heavier hydrocarbon oil into lighter hydrocarbon which comprises subjecting a composite stock derived from said oil and commingled with iinely divided mineral adsorbent towards carbon forming substance to a cracking temperature under superatmospheric pressure, admixing with said composite stock obtaining at said cracking temperature cooler said heavier hydrocarbon oil commingled with nnely divided mineral adsorbent oi spectively as vapor and liquid under accelerated sedimentation by said heavier adsorbent said lighter hydrocarbon and a claried residual iraction, and returning said clarified residual fraction as a portion of said composite stock to cracking conditions as aforesaid.

ARTHUR D. SMITH. 

